1. Field of the Invention
The present invention relates to an active matrix liquid-crystal display device, and more particularly to the configuration of a terminal for electrical connection to an external driving element.
2. Background of the Invention
Active matrix liquid-crystal display devices are known as flat panel displays which save space and operate on a small amount of electrical power.
FIGS. 11(a)-(b) illustrate the concept of an active matrix liquid-crystal display device of the past, and FIG. 11(a) showing the configuration thereof, and FIG. 11(b) showing an equivalent circuit of a TFT substrate.
This active matrix liquid-crystal display device has a thin-film transistor (TFT) substrate 1101 and a color filter substrate (hereinafter referred to as a CF substrate) 1102, in between which is sandwiched a twisted nematic (TN) liquid crystal.
The TFT substrate 1101 has a plurality of pixel electrodes 1106 on a matrix, these pixel electrodes 1106 being connected to thin-film transistors (TFTs) 1109, which act as switching transistors.
Scanning lines 1107 that supply a scanning signal are connected to the gate electrodes of the TFTs, and data lines 1108, which input a display signal, are connected to the drain electrodes, so as to drive the TFTs.
In the peripheral area around the TFT substrate 1101 are provided terminals 1110 in a terminal block 1111 for the purpose of inputting scanning and display signals, these being connected to a signal processing substrate (TAB: taped automated bonding) 1103.
Additionally, the TAB 1103 is connected to an external printed circuit board 1104. The CF substrate 1102 has a RGB color layers and a light-blocking layer for the purpose of blocking light, corresponding to each of the opposing electrodes and pixels.
FIG. 12(a) is a plan view and FIG. 12(b) is a cross-section view of a unit element in an active matrix liquid-crystal display device of the past.
In this display device, the display device is so configured in that the TFT 1203 is formed on a TFT glass substrate 1215, and the TFT 1203 is further comprising a gate electrode 1206 connected to a scanning line 1201, a gate insulation film 1209 formed so as to cover the gate electrode 1206, a drain electrode 1208 connected to a signal line 1202 formed on the gate insulation film 1209, a source electrode 1207 connected to a pixel electrode, a passivation film 1210 formed so as to cover the above-noted elements, and a pixel electrode 1205 connected to the source electrode 1207 via a contact hole 1204 provided in the passivation film. In FIG. 12(b), a black matrix 1213 is shown opposite the TFT 1203, with opposing electrodes 1214 provided therebetween.
In the above-noted active matrix liquid-crystal display device of the past, terminals are provided around the periphery of the display device for making connection between an external substrate TAB and each one of the wirings.
FIGS. 13(a)-(c) show the gate side terminal 1303 connected to the scanning line 1301, and the data side terminal 1304 connected to the data line 1302, FIG. 13(a) being a plan view thereof, and FIG. 13(b) and FIG. 13(c) being cross-section views in the directions indicated by the lines 13(b)-13(b)xe2x80x2 and 13(c)-13(c)xe2x80x2.
The gate side terminal 1303 is provided with a gate layer metal 1306 for forming a gate electrode or the like, onto one region of which is formed a contact hole 1312, a transparent electrode 1310 forming a pixel electrode, for example, being formed as the uppermost layer so as to cover the gate layer metal. A gate insulation film 1307 and a passivation film 1308 are also provided.
A data side terminal 1304 is provided with a data layer metal 1311 forming a drain electrode, for example, on one region of which is formed a contact hole 1312, a transparent electrode 1310 forming a pixel electrode, for example, being formed as the uppermost layer so as to cover the gate layer metal.
These terminals are connected to TAB lead wires by heating and applying pressure to an anisotropic conductive film (ACF) made of a thermally cured adhesive throughout which fine conductive particles are uniformed dispersed.
In a TFT substrate of the past, an inorganic film of a material such as SiN having a thickness of 200 to 400 nm is used as a passivation layer, and there was no overlap between pixel electrodes and wires.
Recently, however, there has been a disclosure, for example, in U.S. Pat. No. 5,641,974, of a technology for causing overlap between a pixel electrode and a wire and broadening the transparent region.
When this is done, in order to reduce the capacitance between the pixel electrode and the signal wires, further patterning is done of an organic film on the passivation film, this being formed to a thickness of 2 to 4 xcexcm.
FIGS. 14(a)-(b) show the scanning line 1401 and the data line 1402. FIG. 14(a) being a plan view thereof, and FIG. 14(b) being a cross-section view in the directions indicated by the lines 14(b)-14(b)xe2x80x2, in which the above-noted organic film is used in an interlayer insulation film.
The process up until the patterning of the passivation film 1410 is the same as in the past. a photosensitive organic film 1411 of acrylic resin or the like is spin-coated onto the passivation film 1410, and this is exposed and developed so as to form a pattern for contact holes 1404 or the like.
When this is done, the organic film in the terminal region is removed, and post-baking is done to thermally harden the organic film.
Finally, a pixel electrode 1405 is formed, and connection is made to the source electrode 1407 of the TFT 1403. In FIG. 13(b), a black matrix 1413 is shown opposite the TFT 1403, with opposing electrodes 1414 provided therebetween.
In the above-noted technology disclosed in U.S. Pat. No. 5,641,974, the transparent region is larger and it is possible to obtain a liquid-crystal display device with brighter and better display performance than in the past.
However, because the passivation film patterning and organic film patterning are performed in different process steps, the number of patterning steps increases, thereby complicating the process and increasing the manufacturing cost.
To solve the above-noted problems, a method was proposed in Japanese Patent Application No. 9-323423, whereby two layers of resist are used to perform organic film patterning and passivation film patterning simultaneously. FIGS. 15(a)-(d) show the process flow using this method to form a contact hole.
Steps up until the formation of the passivation film 1507 are the same (i.e., forming a TFT on a TFT substrate 1501 having a gate electroe 1502, a drain electrode 1505, a source electrode 1506, gate insulation film 1503, an amorphous silicon layer 1504 and a passivation film 1507) as in the prior art (FIG. 15(a)). After continuous application of the organic film 1510 and the resist 1509, exposure and developing are done to simultaneously pattern the resist and wet etch the organic film to frm contact hole 1508 (FIG. 15(b)).
Then, the patterning of the passivation film 1507 is dry-etched with etching has 1511 using the resist 1509 and organic film 1510 as a mask (FIG. 15(c)).
Finally, the resist 1509 only is selectively melted with a specific removing liquid so as to remove the resist (FIG. 15(d)).
When this is done, because one and the same mask is used to pattern the organic film and the passivation film, it is not possible to remove the organic film on the terminal part.
FIGS. 6(a)-(b) show how the TAB 608 and the terminal 601 are connected. In order to distribute the conductive particles 607 uniformly throughout the anisotropic conductive film 606, the diameter of the conductive particles 607 is generally in the range of 2 to 4 xcexcm.
On the other hand, because the thickness of the organic film is 2 to 4 xcexcm, if many conductive particles 607 remain on the organic film 610, the distance between the lower metal layer 602 of the terminal 601 and the tape carrier package 608 (TCP) is larger than the diameter of the conductive particles 607, making it difficult to obtain a good contact between the terminal 601 and the TCP 608.
In U.S. Pat. No. 5,641,974, for the purpose of reducing the capacitance between the pixel electrodes and the signal wires, if when an active matrix substrate has a patterned photosensitive acrylic resin on a passivation film, the number of patterning steps increases by one in comparison with the process for producing an active matrix substrate of the prior art.
To solve this problem, there is disclosed in Japanese Patent Application No. 9-323423, technology whereby two layers of resist are used to performing organic film and passivation film patterning simultaneously, thereby reducing the number of patterning steps to the same as with the prior art.
In this case, because a thick organic film remains on the terminal part, if many conductive particles remain on the organic film, it is not possible to obtain a good contact between the terminal and the TAB.
Accordingly, it is an object of the present invention to provide a terminal structure which makes it possible to obtain a good contact between a terminal and a TAB in an active matrix substrate in which an organic film and a passivation film are patterned simultaneously.
In order to achieve the above-noted objects, the present invention has the following basic technical constitution.
Specifically, the present invention is an active matrix liquid-crystal display device comprising a substrate, a plurality of switching elements and a plurality of pixel electrodes formed in a matrix arrangement on the substrate, scanning lines controlling the switching elements, signal lines supplying data signal to the switching elements, terminals making electrical connections between the scanning and signal lines and external driving elements, and comprising a metal layer which forms the scanning line or the signal line, an interlayer film formed on the metal layer, and a transparent electrode forming the pixel electrode, contact holes formed in the interlayer film, through which the metal layer and the transparent electrode are connected to each other via a transparent electrode formed in the contact hole, and an anisotropic conductive film connecting the active matrix substrate to the external driving elements, the device is further characterized (1) by providing dummy contact holes in the passivation film between adjacent terminals, or by forming the contact holes as a plurality of via holes or contact holes having a diameter that is larger than the diameter of the conductive particles in the anisotropic conductive film or by providing these contact holes in a region outside the region of connection with the external drive elements, so that it is possible to prevent an increase in resistance caused by uneven distribution of conductive particles when an anisotropic conductive film is used for making connections, thereby achieving a good contact in the active matrix liquid-crystal display device.